<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        input:focus{
            background: #ccc;
        }
        /* html:lang(en){
            background: red
        } */
        div{
            width: 100px;
            height: 100px;
            background: red
        }
        div:not(.box){
            display: none
        }
    </style>
</head>
<body>
    <input type="text">
    <div class="box">1</div>
    <div>2</div>
    <div>3</div>
</body>
</html>
<!-- 
    E:lang(en) html
    E:not(选择器)
 -->